In recent years, silver halide photographic light-sensitive materials, particularly light-sensitive materials for photographing use, are required to possess enough high image quality and resolving power to be adapted for high speed light-sensitive materials such as color negative-working light-sensitive materials of ISO 1,000 or small-format cameras such as 110-size cameras or disc cameras.
Regarding high speed light-sensitive materials, various techniques have hitherto been examined such as these to coarsen silver halide grains, to enhance activity of couplers, and to accelerate development. The technique of coarsening silver halide grains has seen almost the maximum limit of sensitivity, and a further great increase in sensitivity cannot be expected from this technique as has been reported by G. C. Farnell and J. B. Chanter, J. Photogr. Sci., Vol. 9, p. 75 (1961). In addition, coarsening of silver halide grains is accompanied by various problems such as deterioration of graininess.
Many investigations have hitherto been made on enhancement of coupler activity. However, their contributions to the sensitivity of light-sensitive material have been insufficient. Further, enhancement of coupler activity causes deterioration of graininess.
As to the technique of accelerating development, it has conventionally been attempted to add various development accelerators such as a hydrazine compound to an emulsion layer or to a developer mainly with respect to black-and-white light-sensitive materials. In many cases, however, this technique involves more fogging or deterioration of graininess and thus is not practical.
Accordingly, it has been proposed to use couplers capable of imagewise releasing a development accelerator or a fogging agent. For example, U.S. Pat. Nos. 3,214,377 and 3,253,924 and Japanese Patent Application (OPI) No. 17437/76 (corresponding to U.S. Pat. No. 4,032,345) (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") disclose couplers capable of releasing thiocyanate ion which accelerates solution physical development. Japanese Patent Application (OPI) No. 150845/82 (corresponding to U.S. Pat. No. 4,390,618) describes couplers capable of releasing acylhydrazines, and Japanese Patent Application (OPI) No. 138636/82 describes couplers capable of releasing hydroquinone, aminophenol developing agent, etc.
It is true that these couplers can provide in some cases more contrast and higher sensitivity, but it has become apparent that, in comparison with the case of not using them, there arises a problem of deterioration of graininess particularly upon low-exposure.
On the other hand, it has become apparent that silver halide grains having an increased silver iodide content can absorb more light rays and provide higher sensitivity but, as is described in Japanese Patent Application (OPI) No. 100846/83, they have the problem of an increase in number of silver halide grains not utilized in image formation (dead grains), which results in deterioration of developability.
Further, since development using p-phenylenediamine type developing agents or using D-76 (which is a developer manufactured and sold by Eastman Kodak Company) or metolascorbic acid surface developer which is popularly conducted at present is the so-called parallel type development in which individual silver halide grains are gradually developed in a parallel manner, the rate of parallel type development of individual grains containing a higher content of silver iodide is much slower than that by the so-called granular type development [using, for example, D-19 or D-72 (which is each a developer manufactured and sold by Eastman Kodak Company)] in which individual silver halide grains are developed at once. Thus, a problem arises in that sufficient sensitivity cannot be attained though the latent image is sufficiently formed or that the graininess in high-exposure portions becomes coarse.